package org.springblade.common.utils;

import org.springblade.core.log.exception.ServiceException;

/**
 * 雪花算法生成全局唯一id 源码解析
 */
public class SnowFlake {

	/**
	 * 起始的时间戳
	 */
	private static final long START_STMP = 1480166465631L;

	/**
	 * 序列号占用的位数
	 */
	private static final long SEQUENCE_BIT = 12;
	/**
	 * 机器标识占用的位数
	 */
	private static final long MACHINE_BIT = 5;
	/**
	 * 数据中心占用的位数
	 */
	private static final long DATACENTER_BIT = 5;

	/**
	 * 每一部分的最大值
	 */
	private static final  long MAX_DATACENTER_NUM = ~(-1L << DATACENTER_BIT);
	private static final  long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
	private static final  long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);

	/**
	 * 每一部分向左的位移
	 */
	private static final  long MACHINE_LEFT = SEQUENCE_BIT;
	private static final  long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
	private static final  long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

	//数据中心
	private long datacenterId;
	//机器标识
	private long machineId;
	//序列号
	private long sequence = 0L;
	//上一次时间戳
	private long lastStmp = -1L;

	public SnowFlake(long datacenterId, long machineId) {

		if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
			throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
		}
		if (machineId > MAX_MACHINE_NUM || machineId < 0) {
			throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
		}
		this.datacenterId = datacenterId;
		this.machineId = machineId;
	}

	/**
	 * 产生下一个ID
	 *
	 * @return
	 */
	public synchronized long nextId() {
		long currStmp = getNewstmp();
		if (currStmp < lastStmp) {
			throw new ServiceException("Clock moved backwards.  Refusing to generate id");
		}

		if (currStmp == lastStmp) {
			//相同毫秒内，序列号自增
			sequence = (sequence + 1) & MAX_SEQUENCE;
			//同一毫秒的序列数已经达到最大
			if (sequence == 0L) {
				currStmp = getNextMill();
			}
		} else {
			//不同毫秒内，序列号置为0
			sequence = 0L;
		}

		lastStmp = currStmp;

		//时间戳部分
		return (currStmp - START_STMP) << TIMESTMP_LEFT
			//数据中心部分
			| datacenterId << DATACENTER_LEFT
			//机器标识部分
			| machineId << MACHINE_LEFT
			//序列号部分
			| sequence;
	}

	private long getNextMill() {
		long mill = getNewstmp();
		while (mill <= lastStmp) {
			mill = getNewstmp();
		}
		return mill;
	}

	private long getNewstmp() {
		return System.currentTimeMillis();
	}

}
